ISOCAM Imaging of Galactic Cirrus: Ursa Major Results
M. A. Miville-Deschênes, F. Boulanger, A. Abergel;
In ISO Beyond Point Sources: Studies of Extended Infrared Emission, 2000, ISO Data Centre, Villafranca del Castillo, Madrid, Spain, R. J. Laureijs, K. Leech and M. F. Kessler, p. 111
ABSTRACT:We have observed three 0.05 square degree fields in the Ursa Major Galactic cirrus with ISOCAM in the LW2 and LW3 filters.
These observations of a
weakly illuminated and diffuse atomic cloud revealed striking variations of
the properties of small dust particles, responsible for the emission in
the 4-18 um range.
First, the combination of ISOCAM images and 21 cm
interferometric data allows us to highlight a rotating filament with a small dust
particles abundance 10 times higher than its surroundings.
We suggest that this
high abundance of small dust particles may be the result of grain
fragmentation in a turbulent flow.
Second, an unexpected variation of the
mid-infrared color was found, at an interface between a fully atomic region and a
denser part of the cloud where molecular hydrogen is formed and
survives.
This color variation suggests that the amplitude of the continuum near 15 um
relative to the aromatic bands rises inside the molecular regions.
This may be
the result of a modification of the dust size distribution or of the
structure of the emitting particles.
The modification of the dust properties in
this region of the Ursa Major cirrus may be at the origin of the formation of
molecular hydrogen.
KEYWORDS: interstellar medium, infrared cirrus, dust, turbulence
CODE: miville-deschenes2000